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authorH. Peter Anvin <hpa@zytor.com>2012-06-21 10:25:03 -0700
committerH. Peter Anvin <hpa@zytor.com>2012-06-21 10:25:03 -0700
commit9751d7627582fc1cc64625d63bde9528c14f1544 (patch)
tree33b0b58eb47f4bda4478c2d658019a1d2986cad8 /arch/x86/realmode
parent2b1b712f050eaf0ac576591281446dc960c0afc5 (diff)
downloadop-kernel-dev-9751d7627582fc1cc64625d63bde9528c14f1544.zip
op-kernel-dev-9751d7627582fc1cc64625d63bde9528c14f1544.tar.gz
x86-64, reboot: Be more paranoid in 64-bit reboot=bios
Be a bit more paranoid in the transition back to 16-bit mode. In particular, in case the kernel is residing above the 4 GiB mark, switch to the trampoline GDT, and make the jump after turning off paging a far jump. In theory, none of this should matter, but it is exactly the kind of things that broken SMM or virtualization software could trip up on. Signed-off-by: H. Peter Anvin <hpa@zytor.com> Link: http://lkml.kernel.org/r/tip-jopx7y6g6dbcx4tpal8q0jlr@git.kernel.org
Diffstat (limited to 'arch/x86/realmode')
-rw-r--r--arch/x86/realmode/rm/reboot.S8
1 files changed, 6 insertions, 2 deletions
diff --git a/arch/x86/realmode/rm/reboot.S b/arch/x86/realmode/rm/reboot.S
index 6bf8fea..f932ea6 100644
--- a/arch/x86/realmode/rm/reboot.S
+++ b/arch/x86/realmode/rm/reboot.S
@@ -22,14 +22,18 @@
ENTRY(machine_real_restart_asm)
#ifdef CONFIG_X86_64
+ /* Switch to trampoline GDT as it is guaranteed < 4 GiB */
+ movl $__KERNEL_DS, %eax
+ movl %eax, %ds
+ lgdtl pa_tr_gdt
/* Disable paging to drop us out of long mode */
movl %cr0, %eax
andl $~X86_CR0_PG, %eax
movl %eax, %cr0
- jmp 1f /* "A branch" may be needed here, assume near is OK */
+ ljmpl $__KERNEL32_CS, $pa_machine_real_restart_paging_off
-1:
+GLOBAL(machine_real_restart_paging_off)
xorl %eax, %eax
xorl %edx, %edx
movl $MSR_EFER, %ecx
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